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She deteriorated rapidly and started vomiting and staring into space, foaming and frothing at the mouth.

Miss Graham rushed Polly to a Havelock North after-hours vet. She was put on a drip and told by the vet it looked to be haemorrhagic gastroenteritis.

"She was basically bleeding blood from her behind like a tap."

Miss Graham took Polly her favourite toy and told her she would see her next morning, "hopefully a little bit better".

But the vet rang in the morning saying Polly had died in her sleep.

The dog owner said she had no children and losing Polly was a "tough blow".

VetEnt Havelock North vet Doctor Alanda Rafferty said she occasionally treated dogs with similar symptoms but this week was "out of the ordinary for vomiting dogs with explosive and bloody diarrhoea".

"I had four cases in three days, one of which, unfortunately, we were unable to save despite doing everything we could ... and another that took five days in hospital before he responded to treatment."

"So far we have found no commonality with all cases, except that they reside in Hawke's Bay."

Dr Rafferty referred the matter to the Ministry for Primary Industries and a spokesman said initial testing had been inconclusive.

They were now testing for all dog diseases present in New Zealand.

Another dog died in January from suspected cyanobacterial poisoning after visiting a local river.

The council issued a statement encouraging people to be cautious when out with their dogs at rivers and ensuring the public were informed about the risks toxic algae posed in summer.

New Zealand Veterinary Association released a statement earlier this year telling people not to feed their dogs scraps because many foods could not be digested the same way humans could.

Dr Rafferty said other Hawke's Bay vet clinics had also seen some cases but were not alarmed at the number.

She said dogs showing those symptoms were often not vaccinated or had potentially fatal parvovirus, or haemorrhagic diarrhoea syndrome.

Polly had a necropsy which showed her death was not a case of any of the above.

The pathologist determined the death was most likely caused by an ingestion of an endotoxin but could not determine what.

Dr Rafferty said it was unknown whether the cases were related, "it just seemed unusual to have so many in a short space of time".

She encourages anyone with dogs presenting similar symptoms to contact either herself or the Ministry.

"It would be great to get to the bottom of the problem."

Miss Graham is getting ready to pick up another puppy in three months' time and she wants to be sure it does not happen again.

She worried her dog may have eaten something from the garden that could have potentially caused her to become ill.

"I would just like other dog owners to be aware that there is a problem out there at the moment and don't want anyone to go through what we have been through."